[piot]

Hi Folks.
I'm Piot, newbie here in this forum and own myself 2 Pontiacs besides other classics from GM and Chrysler.
My Pontiacs are a 1960 Catalina 4dr Flattop 389ci and a 1966 Bonneville 2dr with 421ci.
My 66 Bonneville I bought 3 months ago in AZ.
The pre-owner rebuild the Motor and Transmission in 1991 and drove the car around 50 miles until I bought it 27 years later.
During the years he started it once a while to get all fluids through the system.
The motor was also already broken in after he had it rebuild.
Long story short, I have a temperature problem what I've heard is no surprise on pre-67 Pontiacs.

Today and after 3 months of restoring my Bonneville, I took her out for the first serious ride.
At first I have to say that I put a water temp gauge in the car what seems to be off 20F-30F (compared to my temp gun reading)...made in China crap I guess. BTW the temp sensor is located in the intake.

Anyway, today it was not really hot here in Los Angeles and around 75F.
I was driving the car approx an hour around city, and the temperature stayed stable at 180-190F (gauge reading).
After hitting the freeway and making 70mph+/- for 10 minutes, the car turned into a boiling pot.
The gauge showed 250F and probably only stopped climbing because I pulled over to check the temperature under the hood with my temp gun.
The upper radiator hose close to the thermostat housing read 216F and 196F to the radiator inlet.
The lower hose showed 187F close to the Radiator outlet and 165F to the Block.

I don't know guys but something is not right.
On my other classics, I'm used to see the temperature going down when freeway driving.
I have to add, after exit the freeway and proceed city driving, the temperature won't go down and stayed between 230F-240F (gauge reading) even the car ran steady cool before hitting the freeway.

It's not a condition I feel comfortable driving this car and of course last I need is a head gasket problem on an fresh rebuild motor.
I understand that a fresh rebuild motor runs a lil warmer but mine runs definitely too hot.

In the weeks before I replaced following:
-the motor oil (full synthetic),
-the thermostat (180f),
-rodded out the original radiator,
-put a new fan clutch,
-new water pump.
The original fan shroud is in good condition as well.

My next step would be taking out the thermostat and maybe put in a high flow water pump to see if the temp goes down.

Hope I can get some good advice from you guys.
Any help is appreciated!

Thanks! Piot

[mgarblik]

Have you determined for sure the engine is overheating? Relying on an unreliable Chinese temp gauge as your source for determining this may be leading you down the wrong path. IF your temp gun is accurate and you are seeing around 200 degrees as you indicated after highway driving, I would consider that normal. If the temperature is actually 240 degreres as your gauge says, when you pull over and pick the RPM's up to 1500-2000, the fan should sound like wind tunnel and be completely locked-up to lower the temperature. You didn't say if there was overheating before you changed the coolant pump or if there was any change after changing it. Assuming you have the original timing cover with the two dividing plates, they need to be installed carefully and possibly modified a little to divert the water properly. There is a thread about this. I guess my final point would be to determine for sure accurately, if you have a problem before trying to fix it. That may mean buying and installing a quality gauge like an Autometer/Stewart Warner or similar, or making sure you have an accurate infra-red gun. 200-210 max real temperature would not concern me. I have owned many Pontiacs of that vintage including a 66 421 HO 9 passenger wagon with AC, 8 people on board, hauling a 19 ft. 3500 LB. boat all over the country without ever overheating. Stock cooling system. Good luck.

[MidnightAuto]

I am running a 421 and it was hot too. Just as u state- highway driving was worse. Well above 200. I put in a flowkooler with both pump mods, tightening clearance between impeller and back divider plate, and also with the middle plate for an 8 bolt pump, making it equidistant from the width of the impeller (you can find in this forum). I also put in a 160 Tatar and coldcase radiator. I don’t get above 160 now, no matter what. I think most would say the pump mods are probably the biggest driver of improvement....

[MidnightAuto]

Tstat not tartar. Spell check sucks

[Bill Hanlon]

I'd start with the water pump impeller to divider plate clearance. Lots of talk about the clearance on this forum.

[tom s]

Electric or man gauge?I just pulled a 389 with a 4 bolt water pump out of my 62 GP.I put a 421 30 over in the car with a 8 bolt and a flocooler pump.The car has a original shroud with a non thermo fan.The 389 would gain some temps too close too 230 in stop and go traffic until I put the shroud on.The 421 when I first put it in after the rebuild would get hot around town to about 200ish.Neither would get hot on the highway.The 421 now after a few hundred miles pretty much stays in the 160-180 range.Make sure your timing is inline as if the timing is retarded some they run hot.Im running 12 init and 36 total with 9.5 CR iron heads.The engine has a 068 and the engine pumps the 170-175 range.Tom

[Stuart]

Getting hot at highway speeds can often be caused by a radiator that needs to be flushed or rodded out. Given the limited amount of miles the car has been driven over the last 27 years I wouldn't be surprised if it's clogged up. It may be worth finding a good, old school radiator shop that can give it a good clean.

I went through a similar thing with my '61 Bonneville when I rebuilt it, as well as with a '65 GP I used to own. The radiator in the Grand Prix worked great after it was cleaned out, but unfortunately the radiator in the Bonneville didn't respond to cleaning and I ended up replacing it with a new 'triple flow' style one from US Radiator. It brought the temps right down where they are supposed to be, even on 95 degree days. It looks just like the original, too, except that it doesn't have the Harrison name stamped into the upper tank.

[piot]

Well, I checked the temp on the hoses with two different infra temp guns...both are reading similar numbers.
I don't know what is the best spot to point the temp gun to measure an accurate Temp...but 215F-220F on the upper Radiator Hose close to the Thermostat on a cool evening is too much and who knows how high it would climb when not pulling over the car.
When driving freeway and temp goes up, the motor starts pinging during accelerate and also runs uneven when idling.

Before cleaning out the Radiator, replacing water pump and Tstat from 160F to 180F the engine temp showed similar temperatures.

Long term I will buy a better water temp gauge but I think I can trust my temp gun for first until the problem is fixed.

Originally Posted by mgarblik

Have you determined for sure the engine is overheating? Relying on an unreliable Chinese temp gauge as your source for determining this may be leading you down the wrong path. IF your temp gun is accurate and you are seeing around 200 degrees as you indicated after highway driving, I would consider that normal. If the temperature is actually 240 degreres as your gauge says, when you pull over and pick the RPM's up to 1500-2000, the fan should sound like wind tunnel and be completely locked-up to lower the temperature. You didn't say if there was overheating before you changed the coolant pump or if there was any change after changing it. Assuming you have the original timing cover with the two dividing plates, they need to be installed carefully and possibly modified a little to divert the water properly. There is a thread about this. I guess my final point would be to determine for sure accurately, if you have a problem before trying to fix it. That may mean buying and installing a quality gauge like an Autometer/Stewart Warner or similar, or making sure you have an accurate infra-red gun. 200-210 max real temperature would not concern me. I have owned many Pontiacs of that vintage including a 66 421 HO 9 passenger wagon with AC, 8 people on board, hauling a 19 ft. 3500 LB. boat all over the country without ever overheating. Stock cooling system. Good luck.

[piot]

My problem seems the opposite of yours.
There must be a cause or indicator why the water temp stays solid when driving below 55mph but once going above for a few miles steady, the temp is climbing to the moon.

Originally Posted by tom s

Electric or man gauge?I just pulled a 389 with a 4 bolt water pump out of my 62 GP.I put a 421 30 over in the car with a 8 bolt and a flocooler pump.The car has a original shroud with a non thermo fan.The 389 would gain some temps too close too 230 in stop and go traffic until I put the shroud on.The 421 when I first put it in after the rebuild would get hot around town to about 200ish.Neither would get hot on the highway.The 421 now after a few hundred miles pretty much stays in the 160-180 range.Make sure your timing is inline as if the timing is retarded some they run hot.Im running 12 init and 36 total with 9.5 CR iron heads.The engine has a 068 and the engine pumps the 170-175 range.Tom

[piot]

As mentioned in my first post, I took the Radiator to a shop who cleaned it out.
They said it was clogged up 60%.
Motor is Rebuild in 1990 and driven 50 miles since plus regular start up's during the years.
So I guess flushing the block is no reason.

Originally Posted by Stuart

Getting hot at highway speeds can often be caused by a radiator that needs to be flushed or rodded out. Given the limited amount of miles the car has been driven over the last 27 years I wouldn't be surprised if it's clogged up. It may be worth finding a good, old school radiator shop that can give it a good clean.

I went through a similar thing with my '61 Bonneville when I rebuilt it, as well as with a '65 GP I used to own. The radiator in the Grand Prix worked great after it was cleaned out, but unfortunately the radiator in the Bonneville didn't respond to cleaning and I ended up replacing it with a new 'triple flow' style one from US Radiator. It brought the temps right down where they are supposed to be, even on 95 degree days. It looks just like the original, too, except that it doesn't have the Harrison name stamped into the upper tank.

[geeteeohguy]

Originally Posted by piot

My problem seems the opposite of yours.
There must be a cause or indicator why the water temp stays solid when driving below 55mph but once going above for a few miles steady, the temp is climbing to the moon.

Well, you can lead a horse to water, but..........

You need to check/set the water pump impeller- to- backing plate clearance to no more than 1/8". And go from there. The number one reason these cars run hot. The reason your car gets hotter on the highway is because the engine is generating much more heat at that speed. With inadequate water pump operation, not a surprise. As a side note, Lectric Limited has the correct temperature sending units for our cars. The one I installed in my '65 GTO brought the gauge reading from 225 down to 195....verified by a pyrometer.

[Ragtop Man]

Other stuff to try -

1. Is the fan installed to 'pull' air through? It's an easy mistake and would account for basically 'stalling' air at the radiator. A friend did this on his Mustang. GM has a fan clutch in the parts system (or did) from a Silverado/Sierra pickup that will pull air like a sono***un. Try searching fan clutch in the box and see if it comes up.

2. Are the radiator hoses collapsing at speed? Old rubber in the system will do this.

3. 100X on checking pump, impeller clearance and to be sure you have the good GM cast iron impeller and not the chinese **** stamped crap

4. Do you have the matching sender for the water temp gauge? Installed correctly? Thermostat in place, verified on the bench, and installed correctly?

5. Have you bled all the air from the cooling system? Lots of good posts here on how to do that in your driveway.

6. A thermograph picture of your radiator - possible clogs, etc ruled out?

7. Ruled out a bad head gasket? Any bubbles in the coolant when running at idle?

8. Timing and mixture at cruise speed? Too lean, retarded timing to inhibit knock will cause the engine to run hot

9. Choke tube in intake manifold intact? You can't see it - but - if it is 'lacy' as many are that have not been replaced from 50+ years ago, it is a frustrating, hard to find vacuum leak or as I call it, "West Virginia EGR"

Don't feel bad, these old cars can send symptoms but can't talk to you like the new ones. Just stay at it and you will crack it.

[tom s]

I ALWAYS start with timing!ALWAYS.I have NEVER in 56 years check impeller clearance!I run 160 stat,I run factory shrouds and on iron heads with our 91 piss gas I run 36-38 total timing and 12 init.If your engine was not setup with CR too high to run the proper timing I have found they will run hot.Just for grins,do a hot pumping comp test and also tell us what your total timing is without the vac adv hooked up. JMHO,Tom

[mgarblik]

Originally Posted by Ragtop Man

Other stuff to try -

1. Is the fan installed to 'pull' air through? It's an easy mistake and would account for basically 'stalling' air at the radiator. A friend did this on his Mustang. GM has a fan clutch in the parts system (or did) from a Silverado/Sierra pickup that will pull air like a sono***un. Try searching fan clutch in the box and see if it comes up.

2. Are the radiator hoses collapsing at speed? Old rubber in the system will do this.

3. 100X on checking pump, impeller clearance and to be sure you have the good GM cast iron impeller and not the chinese **** stamped crap

4. Do you have the matching sender for the water temp gauge? Installed correctly? Thermostat in place, verified on the bench, and installed correctly?

5. Have you bled all the air from the cooling system? Lots of good posts here on how to do that in your driveway.

6. A thermograph picture of your radiator - possible clogs, etc ruled out?

7. Ruled out a bad head gasket? Any bubbles in the coolant when running at idle?

8. Timing and mixture at cruise speed? Too lean, retarded timing to inhibit knock will cause the engine to run hot

9. Choke tube in intake manifold intact? You can't see it - but - if it is 'lacy' as many are that have not been replaced from 50+ years ago, it is a frustrating, hard to find vacuum leak or as I call it, "West Virginia EGR"

Don't feel bad, these old cars can send symptoms but can't talk to you like the new ones. Just stay at it and you will crack it.

These are all great suggestions and the timing as well. Couple of other little checks. You never said if the "NEW" fan clutch was locking up as it should and sounding like a wind tunnel when the engine is getting toward 200 degrees +. New fan clutches are notorious for clutching up at temperatures way too high for our old engines. Sometimes don't clutch up fully until 240 degrees. No good for our old engines. There is a thread about how to modify the spring and valve plate on the new clutches to make them lock-up at lower temps. This would of course primarily help in town and at speeds up to 30 MPH or so. Much faster than that, the fan is really just along for the ride and ram air effect through the radiator takes over. You did give me another clue in your posts however. You said the radiator shop told you the core was 60% clogged. What if they actually only got only some of it completely rodded-out and flowing properly? What if it is still say 20-25% clogged? That's a real possibility. I would check off the long list of excellent suggestions above, then if the water pump and divider clearance is proper, fan clutch is working, hoses are not collapsing, timing is correct, as a last resort, I would consider a re-core of the radiator or a replacement. You need a BIG radiator in good condition for that big engine and heavy car. As stated, I have owned a half dozen of these full size 66 cars, 3 with 421 HO's. I used the wagon to tow fully loaded with 8 people, pulling a 3500 LB Sea Ray, 60-65 MPH with a 3.42 rear gear and the AC blasting out frost. Never an overheat situation. OE radiator, fan and shroud. It never ran over 210 degrees, even in 90 degree weather. It can be fixed.